High-speed aerial camera shutter



Aug. 3, 1954 l. w. DOYLE HIGH-SPEED AERIAL CAMERA SHUTTER 5 Sheets-Sheet 2 Filed May 27, 1949 RJMW n MW @m Y ny .LVA. .UBM L Aug. 3, 19514 w. Dos/1 5v 2,685,239

HIGH-SPEED AERIAL CAMERA SHUTTER Filed May 27, 1949 Y 5 Sheets-Sheet 3 ATTORNEYS Aug. 3, 1954 l. w. DOYLE 2,585,239

HIGH-SPEED AERIAL CAMERA SHUTTER Filed May 27, 1949 5 Sheets-Sheet 4 I Il H T. l L

ATTORNEYS Patented Aug. 3, 1954 2,685,239 HIGH-SPEED AERIAL CAMERA SHUTTER Irving W. Doyle, Massapequa, N. Y., assignor to Fairchild Camera and Instrument Corporation Jamaica, N. Y.

Application May 27, 1949, Serial No. 95,849

9 Claims.

This invention relates in general to a combined aerial camera cone and shutter construction, and in particular to a motor-driven, high speed precision shutter attachable to an aerial camera cone and demountable ielative to a fixed optical system supported thereby.

High altitude aerial photography for military mapping or commercial surveying purposes demands increasingly higher degrees of accuracy, which can only be attained by precise relationship of the structural elements of the aerial camera and the provision of accurately precise timing of the operation of the several mechanisrns in the camera which drive the film and shutter.

If the ultimate map made up in the usual manner from a succession of exposures is to have the required degree of sharpness and resolution, the relationship between the lens system and the focal plane of the camera must at all times be precise and the selected shutter speed must be highly accurate, particularly so where color lm is used. In many cameras of the type under consideration attainment of this precise relationship between the lens system and the focal plane is often difficult because of structural complexities, and because it is impossible to remove the shutter without disturbing the lens system, particularly Where the lens system is complex and is constituted by a number of lens elements. It not infrequently occurs in the normal use of such a camera that the shutter has to be removed for one reason or another. Hence it follows that if the sup-porting structure for the lens system and certain structural features of the shutter are such that the shutter may be readily removed and reinstalled without disturbing the lens system, the lens system-focal plane relationship may be maintained as a constant because of the rarely occurring necessity for disturbing the lens system.

It is accordingly among the objects of this invention to provide in an aerial camera of the type under consideration a simple structural relationship among the shutter, lens system and focal plane, whereby to attain the several prerequisites and advantages above set forth.

With respect to shutters for cameras of the type under consideration, various types have been used, including between-the-lens and focal plane shutters, one or the other being used in accordance with the particular requirements to be fullled by the camera. While multiple blade between-the-lens shutters have been developed to a relatively high degree of perfection, they have nevertheless certain inherent disadvantages, particularly where high shutter speeds are prerequisite. Because of the structural relationship of the blades, each blade must be quite thin and accordingly tend to distort and flutter when moved at high speed. Furthermore, such a shutter is not conveniently interchangeable without disturbing the optical system of the camera. Then too, such multiple blade shutters usually must be controlled by retards, shock absorbers, snubbers and the like, greatly complicating the physical structure of the shutter and rendering its operation inaccurate, particularly at high speeds where the factors of acceleration and deceleration are diicult to control. It, of course, goes without saying that such shutters are also characterized by a relatively large number of moving parts made of expensive materials and that require highly skilled labor not only to make but also to assemble and test and maintain.

It is accordingly a further object of this nvention to provide a high speed between-the-lens type shutter that obviates the aforementioned diiiiculties in addition to others in a thoroughly practical, efficient and simple manner.

In the drawing, wherein there is shown one form of the invention,

Figure 1 is an elevation, partly in section, of an aerial camera showing the relationship of the focal plane and the optical system to the shutter, as Well as portions of the shutter operating mechanism;

Figure 2 is an enlarged fragmentary horizontal staggered section taken along the line 2 2 of Figure l;

Figure 3 is a vertical fragmentary section taken along the line 3 3 of Figure 2;

Figure 4 is a horizontal fragmentary section taken along the line 6 4 of Figure 3;

Figure 5 is a vertical fragmentary section taken along the line 5 5 of Figure 2;

Figure 6 is a vertical fragmentary section taken along the line 6 6 of Figure 5;

Figure '7 is a horizontal fragmentary staggered section taken along the line '1 7 of Figure 5;

Figure 8 is a vertical fragmentary section taken along the line 8 8 of Figure 5;

Figure 9 is the wiring diagram of the control circuit for the shutter; and,

Figures 10-15 are a series of curves showing the relationship among the cycles of various portions of the shutter control system.

`Similar reference characters refer to similar parts throughout the several views of the drawing.

In accordance with one embodiment of the invention, the camera cone comprises a single casting of generally inverted frustoconical shape, with its upper surface defining the focal plane of the camera, and its lower portion providing supports for the optical system, which supports are at all times fixed relative to the focal plane. This lower portion of the cone is so formed as to comprise a horizontal compartment for the reception of a between-the-lens shutter which, when in proper operating position, lies between the lens elements of the optical system.

The single blade shutter, together with a conventional iris diaphragm, is mounted on a 'support, which support extends into the above-mentioned cone compartment when the shutter is assembled with the cone. This support, in turn, is carried by brackets or other structural elements which are demountabl'y fastened to the side of the cone and support in proper operative relationship to the various control and driving elements for the shutter blade and iris diaphragm. These supports thus carry a small, high-speed, electric motor which drives a cam into which a shutter blade driving pin may be inserted. When the pin is so inserted, the shutter blade is accelerated and decelerated at positive, predetermined rates to open position, maintained therein for the predetermined period of time, and then again accelerated and decelerated at positive, predetermined rates to closed position. Thus by accurately controlling the motor speed and by properly designing the cam, highly accurate shutter speeds of widely varying values are readily attainable.

Insertion of the shutter blade driving pin into the cam is effected by a spring, this spring acting against the pull of a holding magnet which, upon deenergization, permits the spring bias to effect the shutter blade actuation. Thetime of magnet release is precisely controlled by way of a simple circuit including a vacuum tube, so that the blade driving pin may be released to actuate the shutter blade in precisely timed relation to the high speed rotation of the pin driving cam. Desirably a time delay relay ,controlled solenoid is energized slightly in advance of deenergization of the release magnet, and this solenoid controls a safety catch which effectively locks the blade driving pin out of engagement with the cam should the pin holding magnet or its controlling tube fail for any reason. e

Referring now to the drawing, and to Figure 1 in particular, there is shown a generalized View of an aerial camera comprising a magazine 2B, a cone generally indicated at 2i, a shutter and iris diaphragm assembly, generally indicated at 22, and a shutter blade and iris diaphragm driving and control assembly generally indicated at 23, mounted exteriorly of cone 2l and enclosed by a suitable casing or cover 22. The upper edge or surface 25 of cone 2| may define the focal plane of the camera, while in the lower portion of the cone are mounted upper and lower lens elements 25 and 27, comprising the optical system. The shutter blade and diaphragm assembly 22, when in proper operative position, is disposeclbetween-lens elements 2By and 2l, a manually opera-ble shutter speed control knob 28 being conveniently mounted on the upper portion 2da of the casing 2li. A knob similar to knob 28, but not shown on the drawing, is provided for adjusting the iris diaphragm to set the aperture to the desired value.

Still referring to Fig. l, it may be seen that cone 2l is generally of inverted frustoconical shape, although in certain types of camera it might be desirable that the cone be cylindrical or any other suitable shape. In either event, however, the entire cone structure comprises a single casting whose upper edge 25, as noted, comprises the focal plane of the camera, In the lower portion 21a of the cone are formed integral and preferably annular spaced shelves 2d and 39. The top surface 29a of shelf 29, and the bottorn surface 39a, of shelf 3d are accurately machined relative to upper cone edge 25r so that the axial distance between edge 25 and surface 29a,

CII

and the axial distance between edge 25 and shelf surface 33al accord precisely with predetermined, fixed values for these distances, whereby the shelf surfaces 29a and 33a are accurately related to the focal plane dened by upper cone edge 25. Thus it follows that as all portions of the cone, including shelves 29 and 3G, are integral, i. e. are parts of but a single casting, there can be no variation of the axial distance between the shelf surfaces and the focal plane of the camera. Inasmuch as the lens elements 26 and 2l strictly conform to predetermined formulae, their relation to the focal plane upon installation on shelves 29 and 30 is accurate and fixed. In View of the fact that there is seldom any need to remove lens elements 2S and 2l, their relationship to the focal plane as defined by upper cone edge 2 5 remains a constant.

It will now appear that cone shelves 29 and 3B, with their respective lens elements 2t and 2l, form a narrow compartment 3l within lower cone portion 2id, within which the shutter blade and diaphragm assembly 22 is disposed when the shut.- ter is mounted on the cone. As will be described in detail hereinafter, this shutter blade and diaphragm assembly is readily demountable from its illustrated operative position, and accordingly it follows that in the event of damage to the shutter or its operating mechanism, necessitating its removal for replacement or repair, the assembly 22 may be easily removed without disturbing in any way whatsoever the relationship between the optical system and the focal plane.

In Figure 2 are shown various structural de tails of the shutter blade driving and controlling assembly 23. This assembly includes a main mounting plate 32 (Figure 5) and this plate may have integrally formed therewith or fastened thereto a pair of upright struts 33 and 34 by which the assembly 23 may be fastened to a boss 35 extending laterally and outwardly of lower cone portion 2id. These struts 33 and 3ft are also shown in Figure 3, screws 36 being illustrative means of attaching the struts to boss 35. At one corner of plate 32 (Figure 5) is a post 3l', to the top of which is fastened in any suitable manner a horizontal plate 38, This plate is shaped as shown in Figure 2, and includes a shelflike extension 33 which extends into cone compartment 3l through boss 3E when the shutter is installed. This plate extension 39, as shown in Figure 1, provides together with a lower plate fill an elongated supporting structure for a plate ill on the extremity llla of which are mounted the shutter and iris diaphragm, as will be described hereinafter (see Figure 2).

Plates 39, lo and il are securely held together in assembled relation by a suitable number of screws 42 extending through the three plates. Thus these plates form an elongated shelf-like extension which reaches into cone compartment 3l (Figure 1) between the lens elements 26 and 21 so as to demountably support the shutter blade and iris diaphragm assembly 22 in proper relationship to the lens element. It might here be noted that lower supporting plate All may be integral with or secured to plate 32 in any suitable manner.

As best shown in Figure 8, lower plate 32 is provided with an opening 32a through which the lower portion of a motor 43 extends, the motor casing being provided with a flange 44 which may conveniently be secured to plate 32 by screws 45, thusto hold the motor securely in position thereon. Motor 43 is preferably a shunt Wound reversible motor of fractional horsepower capable of operating at speeds up to 5000 R. P. M. With such a motor it follows that its speed of operation may be controlled with extreme accuracy, this being accomplished in a manner hereinafter to be described.

To the armature of motor 43 is secured an inverted, cup-shaped flywheel 46, in the upper surface of which is cut a cam slot 41 (see Figure 4). This cam slot is of xed radius between points A and B and between points C and D. Between points B and C the cam slot radius decreases in predetermined amount to point B and then increases by predetermined amount from point B to point C, this for a purpose described hereinafter.

Extending outwardly from strut 33 (see Figure 1) are a pair of lugs 48 and 49 which respectively journal the upper and lower ends of a shaft 50. Axial movement of this shaft is conned by a pair of collars 60 and 6| secured to the lower end of shaft 50 on opposite sides of lug 4S). Thus the shaft may rotate in lugs 48 and 49, but may not move axially relative thereto. A follower arm 62 has a hub 63 fastened to shaft 5l] by a set screw 64, this arm accordingly being rotatable relative to the top of flywheel 46, over one side of which the arm lies, as shown in Figure 4. Arm 62 is drilled as at 65 to reciprocably receive a follower pin 66, the upper end of this pin having a flange 61 which limits downward movement of the pin. On the upper end of pin 66 is secured a magnet armature 68, while the pin assembly, including the pin, the flange and the armature, are under a constant downward bias by a relatively strong leaf spring 69 fastened to hub 53. This spring accordingly tends to force pin 66 downwardly toward cam 45 so that the pin may enter cam groove 41.

A link 'itl is pivotally attached to the free end 62a of follower arm 62, this link being slidably disposed between plates 39 and 4i) (Figure l). The outer end a (Figure 2) of link 10 is pivotally attached to the crank arm 'H of a shutter blade 72, this blade being pivotally mounted on a pin 'i3 suitably secured to one or more of plates 39, 40 and 4l. The outer end of plate 12 is sufiiciently large as to completely cover an aperture |20 formed in the end 4|a of plate 4|, this aperture being in axial alignment with the optical system of the camera.

From the foregoing, it will now appear that if the shutter motor is in operation, cam 41 (Figure 4) rotates clockwise. If pin 66 is free to enter the cam slot under the bias of spring 61, it so does and accordingly acts as a follower, following the contour of the cam as it rotates. In view of the fact that the cam is of xed radius from A to B, there is no movement of the follower pin 66 along this portion of the cam. However, from points B to C, the cam radius varies so that as the follower pin follows from point B to B of the cam, it is moved toward the axis of the iiywheel 46 and accordingly swings follower arm 62 clockwise. This clockwise movement of the arm moves link 16 downwardly, as viewed in Figure 2, and accordingly shutter blade l2 clockwise to its open or dotted line position. By varying the contour on opposite sides of point B (Figure 4) of cam 4l', the total open time of the shutter may be predetermined as desired. As the follower pin 55 follows the cam slot from point B to C, reverse movement of the pin, link lil and blade 'i2 (Figure 2) ensues, thus to swing the blade counterclockwise back to its closed or full line position. Thug it follows that for one revolution of flywheel 46 and accordingly cam 4l, the shutter Y blade opens and closes to effect an exposure. In

view of the fact that the cam action is positive, and because there is but a single shutter blade 12, there is little or no tendency of the shutter blade to distort or iiutter during its opening and closing movement. Furthermore, because there are but f-ew moving parts, namely follower arm 62, link 10 and blade 12, and as these parts are small and light, and because of the provision of flywheel 4S, acceleration and deceleration during both the opening and closing of the shutter blade is controlled and smooth, reducing to a negligible minimum any possibility of any of these parts becoming broken or damaged over extended periods of use. inasmuch as the rate of rotation of the motor and accordingly of cam 4l can be governed, as will be described, to a tolerance of l to 2%, the selected shutter speed is highly accurate, thus assuring good photographic results. From the foregoing it follows that as long as follower pin 6s engages cam 4l, the shutter will open and close for each revolution of the cam. This, of course, is undesirable because of the high speed at which the motor operates. made provision for holding follower pin 66 out of cam slot 47 until such time as it is desired to operate the shutter to make an exposure. As shown in Figure 3, a magnet 14 is .suspended from a strap l5 whose opposite ends are attached respectively to lug 48 and a post I6 carried by plate 38. Magnet 74 directly overlies armature 68 so that when the magnet is energized, it pulls the armature upwardly against the bias of spring 69, thus withdrawing follower pin 66 from cam 41. In this position, of course, the pin cannot follow the cam and accordingly the shutter remains closed. When an exposure is desired, magnet 'I4 is rapidly deenergized in a manner that will be described to release armature 68 so that its spring 69 can drive follower pin G5 into the cam slot.

To accomplish this operation of magnet 14, its circuit includes a pair of contacts 'Il and 18, which are mounted in a small Z-shaped bracket 'I9 fastened to plate 38. The lower ends '11a and '18a (see Figure 8) of these contacts 'Il and 'I8 engage a contact disc generally indicated at 30. This disc is fastened as by a screw Si to a gear lill, in turn secured to the upper end of a shaft or post 82, which may conveniently be an extension of the armature shaft of motor 43. As is more clearly shown in Figure 7, contact disc has an outer conductive section Sila and an inner conductive section 80h, which are separated from one another and are fastened to a support 83 (Figure 8) formed of a suitable dielectric material. Thus these sections Sila and Sb (Figure 7) are insulated from one another. Contactor end 11a is always in engagement with section 80h, whereas contact end "Fila overlies section 86a. It will be noted, however, that contact 8b includes a segment 80o which intervenes the ends of section 80a and is insulated therefrom. Accordingly, when disc 80 has rotated to the point where contact end 18d is in engagement with segment 80e, the effect is the same as that of closing a switch, as the two contact ends Ha and 78a are simultaneously in engagement with the conductive section 86h of the contact disc. During this time magnet 'i4 (Figure 3) is energized so that follower pin 66 is withdrawn from cam slot 47 in the manner described above. Because of the small diameter of contact disc 8U, e. g. of the order of 1.25, and because of the high rate of rotation of the contact plate, e. g. up to 5000 R. P, M., the speed of magnet response must be of a very high Hence I have order, if properly timed exposure is to be eifected and double exposure is to be avoided. This vmagnet response is effected in a manner that will be described hereinbelow.

As has been pointed out hereinbefore, it is den sirable to vary the motor speed in order to effect different shutter speeds. To control the rate of rotation of motor d3, I vhave provided the electrical governing mechanism shown in Figures 5, 6 and 7 on sheet ll of the drawing. Inasmuch as this governing mechanism is of conventional nature, it will suffice to include herein but a brief description of its essential parts.

Thus, as shown in Figure 5, plate 32 carries a bracket 31| having a horizontal supporting plate `B and carrying a bracket 33 on a vertical face. Bracket 86 includes a pair of spaced bosses 81 and 88 in which is journaled a stud shaft 89. The upper end of this stud shaft carries a disc 99 on which are mounted the governor contacts 9|. The spacing between these contacts is determined by the vertical position of an arm 92 which bears against the bottom of a pin 93 secured to a threaded plug 94 which is threaded into a collar 95 fastened to plate 85. Plug 95| is drilled to receive the forked end 93 (Figure 6) of an adjusting rod 91, this forked end 95 coacting with a pin 98 extending through the hole in plug 93. As shown in Figure l, rod 91 is of the telescopic type, and has its upper end 5 secured to a tting 99 which is connected to knob 28 in any suitable manner. It may now be seen that as knob 23 is rotated in one direction or the other, rod 91 and accordingly plug 94 (Figure 5) rotate with it, thus to adjust the vertical position of pin 33, and also that of arm 32, hence setting or adjusting the spacing between governor contacts 9|. Variation in the spacing of these contacts determines the speed of rotation of motor 43.

A gear |00 is pinned to shaft 89 between lugs 81 and 88, and this gear meshes with gear ll whose hub |92 is pinned to armature shaft extension 82. Thus, as motor 33 rotates, gear 19| is driven to rotate disc 90. Governor contacts 9| open and close intermittently because of the effect of 'centrifugal action, the ratio of closed time to open time determining the rate of rotation of motor d3. As these contacts close, brushes |03 (Figure 6) are electrically connected, and being in the circuit of motor (i3, cause intermittent energization of the motor. Thus the speed of motor 43 is easily and accurately controlled by manipulation of knob 28 (Figure l), thereby to quickly and accurately set the shutter speed desired.

Under certain circumstances, which will be detailed hereinbelow, it is desirable that follower pin 66 be locked out of engagement with cam 41. To this end, there is provided a safety latch mechanism shown in Figures 2 and 3 of the drawing. This latch mechanism includes a solenoid |913A (Figure 3) carried by a number of posts |95 which extend upwardly from plate 32 (Figure 2). The armature IUS of solenoid |94 is pinned to a latch arm |31 which, as shown in Figure 3, has a hub |38 rockably mounted on shaft 59. The free end of latch arm |91 is generally L-shaped, as shown in Figure 3, and includes a finger H39 which underlies magnet armature 98 (Figure 3) adjacent flange 61. To the left-hand end of latch arm |91, as shown in Figure 2, is attached one end of a spring IIE, which spring extends through the web 34a of bracket 8d, and has its other end fastened to 8 a screw threaded `into this (bracket.V Spring H9 accordingly Vconstantly biases latch arm |94 counterclockwise, tending to move latch finger |99 toward the axis of the follower pin flange 61 (Figure 3). Of course, when solenoid |94 is energized, it swings arm m1 clockwise against the pull of spring Hi! so that latch fing-'er |09 is removed from flange B1.

As shown in Figures 4 and 8, the depth of cam slot 31 varies from a maximum at point A to a minimum at point D. In fact, at point D the slot terminates. Accordingly, as follower pin 66 rides along the slot from point A to point D, it is ultimately pushed upwardly, and with it armature 53. Flange 61 (Figure 3) lifts with the follower pin t6 vand accordingly when the pin rides out of the cam slot, the bottom of the flange is above the top of latch finger |09. If solenoid |013 is deenergized at this time, latch finger |09 will be swung beneath flange 61 by spring H0, thus locking follower pin 66 in its uppermost position from which it cannot move until solenoid |94 is reenergized. It should also be noted that this lifting of follower pin E6 in the slot end of cam slot 31 moves armature 68 very close to magnet 1li, facilitating attraction of the :armature when the magnet is reenergized.

As noted hereinbefore, end 41a (Figure 2) of supporting plate il provides a support for an iris diaphragm, diagrammatically and generally indicated at |2. The diaphragm includes a large gear H3 which is driven through a gear train comprising gears Hd, |5, |65 and |1 by a pinion i8 fastened to the lower end of an operating rod H9. This rod is preferably of a telescopic type similar to shutter speed adjusting rod 91, and has secured to its upper end an operating knob (not shown) similar to operating knob 28 (Figure l) and located adjacent thereto. The gear train connecting pinion ||8 to diaphragm gear ||3 is mounted between plates 39 and d in any suitable manner, and accordingly there is provided a simple but effective means for adjusting the diaphragm to the desired aperture.

As previously explained, an exposure is made when holding magnet 13 is deenergized. Thisr deenergization is effected by a circuit (Figure 9) which includes the contacts 11a and 18a, the safety latch solenoid Hifi, a vacuum tube generally indicated at |25, and a trip switch |23. The tube |25 is a conventional triode having a, plate |25a., a grid |2517 and a cathode |250. The plate e is connected by a lead |28 to one side of the magnet 1d, the other side of the magnet being connected by a lead |29 to the positive terminal of a battery |21. The cathode |250 is connected by a lead |39 to the grounded negative terminal of battery |21. A resistance |3| is connected between grid |2513 and cathode |25c by leads |32 and |33. The right side of a condenser |34 is connected by a lead |33 to grid |25b, and the left side of the condenser by a lead |36 to the left side of a second condenser |31. The right side of condenser |31 is connected by a lead |38 to lead |33, and thence to cathode |25c. Condenser |31 is larger than condenser |34, for reasons which will be explained hereinafter.

Contact 11a is connected by a lead |39 to the left side of condenser |31 and contact 18a by a lead l!) to a switch |41, which is in turn connected to the rightl side of condenser |31 by a lead |42. A resistance |3 is connected by leads Mii and |45 to the contact 11a and to the positive terminal of battery |21, respectively.

Switch |4| is operated by a time delay relay |46, which is connected at one end by a lead M1 t0 the negative terminal of battery |21, and by a lead |48 to one contact of trip switch |25. The other contact of switch |26 is connected by a lead |49 to the positive terminal of battery |21. Solenoid |623 is also connected in series with the battery and switch 26 by leads |553 and |5l.

Trip switch 26 may be located in the camera magazine so as 'to be periodically closed to initiate a complete cycle of operation of the camera. When the switch closes, a circuit is established from battery |21 through the switch and solenoid |04, causing the solenoid to be energized and the safety latch lill to be released.. At the same time relay |46, which is of the time delay type, is energized, causing switch |4| to close after a brief interval, which assures that safety latch 61 has been released. An exposure is obtained when switch Mi and the switch comprising lcontacts 11a and 18a close at th: same time, as will now be explained.

In the steady state condition, condensers |34 and |31 are charged through resistances |43 and |3| to the potential of battery |21. As a result, the left side of condensers |315 and |31 have a positive potential, and the right sides of the condensers are at ground potential. Current will therefore dow through tube |25 and holding magnet 14. When switch I4! and the contacts 11a and denser |31 is short-circuited through the switches so that the left side of condenser i3? immediately drops to ground potential. Condenser |34 also starts to discharge through the switches IM and 11a-18a and resistance ISI, but its discharge lags behind that of condenser |31, because of its relatively small capacitance and the retarding effect of resistance 3|. The condenser |34, therefore, is still considerabl i charged when contacts 11d and 18d open, and is able to discharge only slowly through condenser |31, which has a large capacitance. Accordingly, the right side of condenser |34 drops to a potential below ground and causes tube |25 to be cut off. This causes very rapid deenergization of holding magnet 1li so that follower pin 65 (Figure 4) enters cam slot d1, causing actuation of the shutter, as described.

Tube |25 (Figure 9), however, is cut off only for an instant, because the circuit between contacts I' 17a and 18a is broken, as described. Hence, condensers 34 and |31 are immediately recharged by battery |21 through resistances |43 and |3| in a direction to cause the grid side of resistance I3! to be slightly positive with respect to the cathode 31.1'

side. The resultant current through tube |25 causes magnet id to be energized and the pin 66 withdrawn from cam slot 41, precluding shutter actuation.

As may be seen from Figure 10, trip switch |25 is energized for a much longer period during each cycle of operation than the motor switch Mamma, the closing of switches H5 and 11d- 18d being represented at |52 and |53, respectively. Accordingly, the switch 11a- 18a will close a number of times for one closing of switch $26. However, an exposure will be obtained only when switch 11a-18a closes for the rst time after the closing of switch |25, since for subsequent closings of the motor switch condensers |34 and will not be suiiiciently recharged to out off tube |25. The voltage on the grid |25b is diagrammatically indicated by curve |54, which shows the relatively great voltage drop |54a when the switch 11a-18a rst closes after the closing 15a are closed at the same time, conof trip switch |25, and the smaller voltage drops l'b resulting from subsequent closings of the motor switch. The voltage drop across condenser l 31 is diagrammatically indicated at curve i 55; the condenser discharge causing an exposure to be made is indicated at |55a, and subsequent short circuits are indicated at |5517. The drop in the current through magnet 'is is indicated by curve |56, the current drop EEE@ corresponding to the voltage drop |5lia, and the current drops |5Sb corresponding to the voltage drops |545. Line |51 shows the current below which magnet 1f! is deenergized to effect shutter operation, and, as may be seen, only the current drop |5-5a is of suiiicient magnitude to obtain this exposure. Accordingly, for each closing of switch |25, only one shutter exposure, diagrammatically indicated at |58, is obtained. When switch |25 opens, battery |21 is able to completely recharge condensers |34 and so that the circuit is reconditioned for shutter operation when switch again closes to initiate another cycle of operation.

Accordingly I have provided a high speed aerial camera shutter which attains the several objects set forth hereinabove in a thoroughly practical and efficient manner.

As many possible embodiments may be made of the above invention, and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim:

in shutter construction the combination of a continuously operable motor, a cam coupled to said motor so as to be continuously driven thereby, an opaque shutter, means normally holding said shutter stationary, a driving mechanism coupled to said shutter to impart motion thereto, cam follower means on said shutter driving mechanism engageable with said cam, means normally holding said follower from engagement with said cam, and means selectively operable to effect engagement between said follower and said cam to operate said shutter.

2. In apparatus for controlling the passage of radiation through an optical system, the combination of a motor including a continuously rotatable shaft, a cam coupled to the shaft of said motor so as to be continuously rotated thereby, an opaque shutter to interrupt passage of radiation through the optical system, means normally holding said shutter stationary, driving means coupled to said shutter so as to impart motion to said shutter when said driving means is operated, a cam follower on Said shutter driving lmeans engageable with said continuously rotated cam, means normally holding said cam follower out of engagement with said cam, means selectively operable to effect engagement between said follower and said rotating cam to operate said shutter driving means, and means for disengaging follower from said cani after one revolution thereof.

3. In apparatus for controlling the passage or" light through an optical. system, the combination of a variable speed electric motor, a rotatable cam continuously driven by said znotor, an opaque shutter, means normally holding said shutter stationary in a position to obstruct the passage of light, driving means coupled to said shutter to move said shutter from and to said normal position, a cam follower coupled to said shutter driving means and engageable with saidv rotatable cam, means normally restraining said follower from engagement with said cam, means optionally operable to releasel said restraining means, means operable upon release of saidv restraining means to effect engagement' between said follower and said continuously driven cam,

Vand means to disengage said follower from said cam after one revolution thereof.

4. In apparatus for controlling the passage of light through the optica-l' system of a camera, the combination of. a variable speed motor, a cam coupledtosaid motorY so as to be driven thereby, an opaque shutter, a driving mechanism including a cam follower coupled to said shutter, means biasing said follower toward engagement with said cam, energizable restraining means normally holding said follower out of engagement with said cam, means under the-control of an operator for interrupting energization of said restraining means to effect engagement between said ca-m and said' follower, and means for disengaging said follower from said cam after each operation thereof.

5. In apparatus for controlling the. passage of light through the optical system of acamera, the combination of a motor, a. cam driven by said motor, an opaque shutter interposed in the optical path, means normally holding said shutter stationary, acam follower coupled tovsaid shutter and engageable with said cam to impart motion to said shutter, electromagnetic means normally energized toA restrain said follower from engagement with said cam, means under the optional control of an operator for de-energizingsaid electromagnetic means, means operable upon deenergization of said electromagnetic means to effect. engagement between said follower and said cam, means operable after each engagement of said follower with said cam to re-energize said electromagnetic means, and means including said electro-magnetic means 11e-energized to disengagev saidv follower from said cam.

6, In apparatus for controlling the passage of light through the optical system of a camera, the combination of an opaque shutter, means normally holding said shutter stationary in a positionV to obstruct they passage of light through the optical system, a link coupled to said shutter to move said shutter from and to said normal position,` a cam follower coupled to said link, a motor, a cam driven by said motor, means biasing said cam follower toward engagement with said cam, electromagnetic means normally energized to restrain said follower from engagement with said L cam,lelectronic means for momentarily de-energizing said electromagnetic means to allow said cam follower to engage said cam, means including said electronic means for re-energizing said electro-magnetic means after each momentary de-energization thereof, and means including said electromagnetic means re-energized for disengaging saidv follower from said cam.

7. In apparatus for controlling the passage of light through the optical system of a camera, the combination of a shutter blade pivotally mounted about an axis substantially parallel to the axis of the camera optical system, means normally holding said shutter stationary in a position to obstruct the` passage of light through the optical system, a link coupled to said shutter to move sai@l shutter from and to said normal position, a cam follower coupled to said link, a continuously operating electric motor, a cam coupled to the shaft of said motor so as to be continuously rotated thereby, means normally biasingy said cam follower towards engagement with said cam, electromagnetic means normally energized to holdv said cam follower against said biasing means from engagement with said cam, and electronic means under the control of an operator for momentarily releasing said electromagnetic means to allow said cam follower to engage said rotating cam through one revolution thereof, whereby said shutter is rapidly moved from and restored to its normal position.

8. In apparatus for controlling the passage of light through an optical system, the combination of a shutter normally interposed in the optical system to obstruct the passage of light therethrough, a link coupled to said shutter, a ca-m follower coupled to said link, a variable speed electric motor, a continuously rotatable `cam coupled to the shaft of said motor and rotated thereby, biasing means urging said cam follower towards engagement with said cam, electromagnetic restraining means normally energized to restrain said follower from engagement with said cam, electronic means including a thermionic valve under the control of an operator for momentarily cle-energizing said electro-magnetic means to allow said cam follower to engage said rotating cam through one revolution thereof, and a safety latch movable into engagement with-said cam follower restraining means for holding said follower from engagement with said cam when said latch is so moved.

9. In apparatus for controlling the passage of light through an optical system, the combination of an opaque shutter blade pivotally mounted on an axis substantially parallel to the axis of the optical system, means normally holding said shutter stationary in a position to obstruct the passage of light through the system, a link coupled tosaid shutter to move said shutter from and to said normal position, a cam follower coupled to said link, a continuously operating variable speed electric motor, a continuously rotatable cam coupled to the shaft of said motor so as to be continuously rotated thereby, biasing means normally urging said cam follower towards engagement with said cam, electromagnetic restraining means normally energized to hold said follower from engagement with. said cam, electronic meansincluding a thermionic valve under the control of anop-erator for momentarily releasing said restraining means to allow said cam follow-er to engagelsaidrotating cam, means including said electronic means for re-energizing said electromagnetic means to disengage said follower from said cam after one revolution thereof, a safety latch normally interposed between said follower and said cam, and electromagnetic means operable to remove said safety latch from its normal position prior to release of said restraining means.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 688,103 Edgecomb Nov. 28, 1899 1,620,304 Underwood Mar. 8, 1927 1,887,193 Merle Nov. 8, 1932 2,347,700 Aronoif May 2, 1944 2,359,116 Johnson Sept. 26, 1944 2,371,072 Simmon et al Mar. 6, 1945 2,383,381 Hammond Aug. 2l, 1945 2,399,476 Doyle et al Apr. 30, 1946 2,448,736 Rabinowitz Sept. 7, 1948 

